1. Field of the Invention
This invention relates to tubular textile braids forming parts of electric cables or other elongate bodies (such as optical cables and flexible pipes). It is more specifically concerned with braids formed from yarns comprising many monofilaments of synthetic textile material. p 2. Description of the Related Art
Such braids are used to achieve pressure-withstand characteristics and/or for aesthetic reasons, and in either case it is desirable to achieve as nearly as possible 100% coverage of textile material over the underlying core. This is in conflict with the practical requirements for adequate tensile strength and abrasion resistance, which would otherwise suggest the use of twisted yarns, and in many cases yarns with practically no twist have been used. Such yarns are susceptible to fraying and breakage in the braiding machine, and this susceptibility not only limits the running speed of the machine but also gives rise to frequent interruptions and consequent down-time.
In a braiding machine, yarns are divided into two groups, usually referred to as "upper" and "lower" on the assumption that the axis of the machine is vertical; yarns of the lower group have to be moved around a sinuous path in order to cross over and under those of the upper group to weave the required braid pattern, and this inevitably exposes them to greater abrasion than those of the upper group; we have now recognized that this difference creates an opportunity to increase braiding speed and/or reduce down-time without unacceptably reducing yarn coverage.